U.S. patent number 5,964,742 [Application Number 08/929,808] was granted by the patent office on 1999-10-12 for nonwoven bonding patterns producing fabrics with improved strength and abrasion resistance.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to David Lee Fuqua, Ann Louise McCormack, Kevin Edward Smith.
United States Patent |
5,964,742 |
McCormack , et al. |
October 12, 1999 |
Nonwoven bonding patterns producing fabrics with improved strength
and abrasion resistance
Abstract
There is disclosed a thermal bonding pattern for nonwoven fabric
comprising a pattern having an element aspect ratio between about 2
and about 20 and an unbonded fiber aspect ratio of between about 3
and about 10. It has been unexpectedly found that such a fabric has
a higher abrasion resistance and strength than a similar fabric
bonded with different bond patterns of similar bond areas. This
combination of strength and abrasion resistance has long been
sought after.
Inventors: |
McCormack; Ann Louise (Cumming,
GA), Fuqua; David Lee (Huntsville, AL), Smith; Kevin
Edward (Knoxville, TN) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
|
Family
ID: |
25458484 |
Appl.
No.: |
08/929,808 |
Filed: |
September 15, 1997 |
Current U.S.
Class: |
604/380; 428/198;
604/358 |
Current CPC
Class: |
D04H
1/54 (20130101); A61F 13/5148 (20130101); Y10T
428/24826 (20150115); A61F 2013/15292 (20130101); A61F
2013/15406 (20130101) |
Current International
Class: |
D04H
1/54 (20060101); A61F 13/15 (20060101); A61F
013/15 () |
Field of
Search: |
;604/358,380
;428/198 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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97/11662 |
|
Apr 1997 |
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WO |
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97/11661 |
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Apr 1997 |
|
WO |
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97/24482 |
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Jul 1997 |
|
WO |
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Other References
S N. 08/754,519 filed Dec. 17, 1997, "Pattern-Unbonded Nonwoven Web
and Process for Making the Same". .
S. N. 08/929,432 filed Sep. 15, 1997, "Breathable Barrier Composite
Useful as an Ideal Loop Fastener Component". .
S. N. 08/929,561 filed Sep. 15, 1997, "Stretch-Pillowed Bulked
Laminate Useful as an Ideal Loop Fastener Component"..
|
Primary Examiner: Weiss; John G.
Assistant Examiner: Ruhl; Dennis
Attorney, Agent or Firm: Robinson; James B.
Claims
What is claimed is:
1. A pattern bonded nonwoven fabric comprising a nonwoven fabric
having a pattern of bonds providing a bond area, said pattern
having an element aspect ratio between about 2 and about 20 and an
unbonded fiber aspect ratio of between about 3 and about 10.
2. The nonwoven fabric of claim 1 which has a bond area between
about 5 and about 30 percent.
3. The nonwoven fabric of claim 1 which has a bond density between
about 50 and about 200 pins per square inch.
4. The nonwoven fabric of claim 1 which has been thermally
bonded.
5. The nonwoven fabric of claim 4 having an abrasion resistance and
strength greater than a fabric having a similar bond area but an
element aspect ratio less than 2.
6. The nonwoven fabric of claim 4 having an abrasion resistance and
strength greater than a fabric having a similar bond area but
having an unbonded fiber aspect ratio less than 3.
7. The fabric of claim 4 which is stretched to produce
perforations.
8. A diaper comprising the fabric of claim 4.
9. A wiper comprising the fabric of claim 3.
10. An incontinence product comprising the fabric of claim 4.
11. A feminine hygiene product comprising the fabric of claim
4.
12. An infection control product comprising the fabric of claim
4.
13. A laminate comprising a nonwoven fabric having the pattern of
claim 1 and a film, thermally bonded together.
14. The laminate of claim 13 which is stretched to produce
perforations.
15. A thermally bonded nonwoven fabric comprising nonwoven fabric
having a pattern of bonds and having a bond area, said pattern
having an element aspect ratio between about 7 and about 15 and an
unbonded fiber aspect ratio of between about 8 and about 3.
16. The thermally bonded nonwoven fabric of claim 15 having a bond
area of less than about 30 percent.
17. The thermally bonded nonwoven fabric of claim 15 wherein said
element aspect ratio is between 8 and 12.
18. A thermally bonded nonwoven fabric comprising nonwoven fabric
having a pattern of bonds and having a bond area, said pattern
having an element aspect ratio between about 8 and about 12, said
bond area being between about 15 and 20 percent, and an unbonded
fiber aspect ratio between about 6 and about 4.
19. A laminate comprising a film and the nonwoven fabric of claim
18.
20. The laminate of claim 19 further comprising apertures at said
bonds produced by stretching said laminate.
21. The fabric of claim 18 wherein said pattern has a bond density
between about 75 and about 150 pins per square inch.
Description
FIELD OF THE INVENTION
The present invention relates to the field of nonwoven fabrics like
those produced by the meltblowing and spunbonding processes. Such
fabrics are used in a myriad of different products such as
garments, personal care products, infection control products,
outdoor fabrics and protective covers.
BACKGROUND OF THE INVENTION
Nonwoven fabrics produced by the meltblowing and spunbonding
process have found great utility in many diverse applications from
car and boat covers to incontinence products. Different attributes
or properties of the fabric are required depending on the
application. A car cover, for example, must have great tensile
strength and resistance to ultraviolet radiation, while a feminine
hygiene product must exhibit great absorbency and softness.
Developing just the right combination of properties for the
application is a complex task requiring the focused attention of
many highly qualified individuals.
The bonding pattern used in either bonding the fibers of the
nonwoven fabric to itself or in bonding the nonwoven fabric to
other material layers can cause great changes in the fabric
properties. Bonding patterns with large bond areas, for example,
tend to make a strongly bonded but rough feeling fabric. Those with
small bond areas tend to make soft feeling but very weak
fabric.
Various attempts have been made at overcoming the disadvantage
seemingly inherent in higher bond areas, i.e. decreased softness.
One such attempt is taught in U.S. Pat. No. 5,620,779 to Levy and
Mcormack and is a nonwoven fabric with a bond pattern having a
certain required spacing ratio which is then stretched to produce
ribs.
A number of treatments have also been developed to soften nonwoven
fabrics such as multiple washings and chemical treatments.
There remains a need, however, for an unribbed fabric without
chemical treatments having good bonding strength (i.e. tensile
strength and abrasion resistance) yet also having good fabric
softness without excessive bonding area.
Accordingly, it is an object of this invention to provide a
nonwoven fabric with a bonding area comparable to fabrics bonded
with known patterns yet having greater softness and comparable or
better tensile strength and abrasion resistance.
SUMMARY OF THE INVENTION
The objects of the invention are met by a thermal bonding pattern
for nonwoven fabric comprising a pattern having an element aspect
ratio between about 2 and about 20 and an unbonded fiber aspect
ratio of between about 3 and about 10. It has been unexpectedly
found that such a fabric has a higher abrasion resistance and
strength than a similar fabric bonded with different bond patterns.
In alternative embodiments, the fabric may be perforated or
apertured by stretching after bonding according to known
techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a drawing of a bonding pattern satisfying the
requirements of this invention and called the S-weave pattern.
FIG. 2 is a drawing of a bonding pattern according to U.S. Pat. No.
3,855,046 known as an Expanded Hansen-Pennings or EHP pattern.
FIG. 3 is a drawing of a bonding pattern known in the art as a wire
weave pattern.
FIG. 4 is a drawing of a pattern according to U.S. patent
application Ser. No. 08/754,419 known as a Point Unbonded Pattern
or PUB.
DEFINITIONS
"Hydrophilic" describes fibers or the surfaces of fibers which are
wetted by the aqueous liquids in contact with the fibers. The
degree of wetting of the materials can, in turn, be described in
terms of the contacts angles and the surface tensions of the
liquids and materials involved. Equipment and techniques suitable
for measuring the wettability of particular fiber materials or
blends of fiber materials can be provided by a Cahn SFA-222 Surface
Force Analyzer System, or a substantially equivalent system. When
measured with this system, fibers having contact angles less than
90.degree. are designated "wettable" or hydrophilic, while fibers
having contact angles equal to or greater than 90.degree. are
designated "nonwettable" or hydrophobic.
"Layer" when used in the singular can have the dual meaning of a
single element or a plurality of elements.
As used herein the term "nonwoven fabric or web" means a web having
a structure of individual fibers or threads which are interlaid,
but not in an identifiable manner as in a knitted fabric. Nonwoven
fabrics or webs have been formed from many processes such as for
example, meltblowing processes, spunbonding processes, and bonded
carded web processes. The basis weight of nonwoven fabrics is
usually expressed in ounces of material per square yard (osy) or
grams per square meter (gsm) and the fiber diameters useful are
usually expressed in microns. (Note that to convert from osy to
gsm, multiply osy by 33.91).
As used herein the term "microfibers" means small diameter fibers
having an average diameter not greater than about 75 microns, for
example, having an average diameter of from about 0.5 microns to
about 50 microns, or more particularly, microfibers may have an
average diameter of from about 2 microns to about 40 microns.
Another frequently used expression of fiber diameter is denier,
which is defined as grams per 9000 meters of a fiber and may be
calculated as fiber diameter in microns squared, multiplied by the
density in grams/cc, multiplied by 0.00707. A lower denier
indicates a finer fiber and a higher denier indicates a thicker or
heavier fiber. For example, the diameter of a polypropylene fiber
given as 15 microns may be converted to denier by squaring,
multiplying the result by 0.89 g/cc and multiplying by 0.00707.
Thus, a 15 micron polypropylene fiber has a denier of about 1.42
(15.sup.2 .times.0.89.times.0.00707=1.415). Outside the United
States the unit of measurement is more commonly the "text", which
is defined as the grams per kilometer of fiber. Tex may be
calculated as denier/9.
"Spunbonded fibers" refers to small diameter fibers which are
formed by extruding molten thermoplastic material as filaments from
a plurality of fine, usually circular capillaries of a spinneret
with the diameter of the extruded filaments then being rapidly
reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et
al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No.
3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394
to Kinney, U.S. Pat. No. 3,502,763 to Hartman, and U.S. Pat. No.
3,542,615 to Dobo et al. Spunbond fibers are generally not tacky
when they are deposited onto a collecting surface. Spunbond fibers
are generally continuous and have average diameters (from a sample
of at least 10) larger than 7 microns, more particularly, between
about 10 and 20 microns.
"Meltblown fibers" means fibers formed by extruding a molten
thermoplastic material through a plurality of fine, usually
circular, die capillaries as molten threads or filaments into
converging high velocity, usually hot, gas (e.g. air) streams which
attenuate the filaments of molten thermoplastic material to reduce
their diameter, which may be to microfiber diameter. Thereafter,
the meltblown fibers are carried by the high velocity gas stream
and are deposited on a collecting surface to form a web of randomly
disbursed meltblown fibers. Such a process is disclosed, for
example, in U.S. Pat. No. 3,849,241. Meltblown fibers are
microfibers which may be continuous or discontinuous, are generally
smaller than 10 microns in average diameter, and are generally
tacky when deposited onto a collecting surface.
As used herein, the term "coform" means a process in which at least
one meltblown diehead is arranged near a chute through which other
materials are added to the web while it is forming. Such other
materials may be wood pulp, superabsorbent particles, cellulose or
staple fibers, for example. Coform processes are shown in commonly
assigned U.S. Pat. No. 4,818,464 to Lau and U.S. Pat. No. 4,100,324
to Anderson et al. Webs produced by the coform process are
generally referred to as coform materials.
"Conjugate fibers" refers to fibers which have been formed from at
least two polymer sources extruded from separate extruders but spun
together to form one fiber. Conjugate fibers are also sometimes
referred to as multicomponent or bicomponent fibers. The polymers
are usually different from each other though conjugate fibers may
be monocomponent fibers. The polymers are arranged in substantially
constantly positioned distinct zones across the cross-section of
the conjugate fibers and extend continuously along the length of
the conjugate fibers. The configuration of such a conjugate fiber
may be, for example, a sheath/core arrangement wherein one polymer
is surrounded by another or may be a side by side arrangement, a
pie arrangement or an "islands-in-the-sea" arrangement. Conjugate
fibers are taught, for example, in U.S. Pat. No. 5,382,400 to Pike
et al. For two component fibers, the polymers may be present in
ratios of 75/25, 50/50, 25/75 or any other desired ratios. The
fibers may also have shapes such as those described in U.S. Pat.
No. 5,277,976 to Hogle et al. which describes fibers with
unconventional shapes. "Biconstituent fibers" refers to fibers
which have been formed from at least two polymers extruded from the
same extruder as a blend. The term "blend" is defined below.
Biconsfituent fibers do not have the various polymer components
arranged in relatively constantly positioned distinct zones across
the cross-sectional area of the fiber and the various polymers are
usually not continuous along the entire length of the fiber,
instead usually forming fibrils or protofibrils which start and end
at random. Biconstituent fibers are sometimes also referred to as
multiconstituent fibers. Fibers of this general type are discussed
in, for example, U.S. Pat. No. 5,108,827 to Gessner.
As used herein "thermal point bonding" involves passing a fabric or
web of fibers to be bonded between a heated calender roll and an
anvil roll. The calender roll is usually, though not always,
patterned in some way so that the entire fabric is not bonded
across its entire surface, and the anvil roll is usually flat. As a
result, various patterns for calender rolls have been developed for
functional as well as aesthetic reasons. One example of a pattern
has points and is the Hansen-Pennings or "H&P" pattern with
about a 30% bond area with about 200 pins/square inch as taught in
U.S. Pat. No. 3,855,046 to Hansen and Pennings. The H&P pattern
has square point or pin bonding areas. Another typical point
bonding pattern is the expanded Hansen-Pennings or "EHP" bond
pattern which produces a 15% bond area. Another typical point
bonding pattern designated "714" has square pin bonding areas
wherein the resulting pattern has a bonded area of about 15%. Other
common patterns include a diamond pattern with repeating and
slightly offset diamonds with about a 16% bond area and a wire
weave pattern looking as the name suggests, e.g. like a window
screen, with about an 18% bond area. Typically, the percent bonding
area varies from around 10% to around 30% of the area of the fabric
laminate web. As in well known in the art, the spot bonding holds
the laminate layers together as well as imparts integrity to each
individual layer by bonding filaments and/or fibers within each
layer.
As used herein "pattern unbonded" or interchangeably "point
unbonded" or "PUB", means a fabric pattern having continuous
thermally bonded areas defining a plurality of discrete unbonded
areas. The fibers or filaments within the discrete unbonded areas
are dimensionally stabilized by the continuous bonded areas that
encircle or surround each unbonded area, such that no support or
backing layer of film or adhesive is required. The unbonded areas
are specifically designed to afford spaces between fibers or
filaments within the unbonded areas. A suitable process for forming
the pattern-unbonded nonwoven material of this invention includes
providing a nonwoven fabric or web, providing opposedly positioned
first and second calender rolls and defining a nip therebetween,
with at least one of said rolls being heated and having a bonding
pattern on its outermost surface comprising a continuous pattern of
land areas defining a plurality of discrete openings, apertures or
holes, and passing the nonwoven fabric or web within the nip formed
by said rolls. Each of the openings in said roll or rolls defined
by the continuous land areas forms a discrete unbonded area in at
least one surface of the nonwoven fabric or web in which the fibers
or filaments of the web are substantially or completely unbonded.
Stated alternatively, the continuous pattern of land areas in said
roll or rolls forms a continuous pattern of bonded areas that
define a plurality of discrete unbonded areas on at least one
surface of said nonwoven fabric or web. Alternative embodiments of
the aforesaid process includes pre-bonding the nonwoven fabric or
web before passing the fabric or web within the nip formed by the
calender rolls, or providing multiple nonwoven webs to form a
pattern-unbonded laminate. The point unbonded pattern and process
are described in U.S. Pat. application Ser. No. 08/754,419 and an
example may be seen in FIG. 4.
As used herein, the term "element aspect ratio" refers to the ratio
between the length of an element or pin in a bonding pattern to the
width of the same element, calculated as length of an element
measured along its centerline divided by width of the element.
As used herein, the term "unbonded fiber aspect ratio" refers to
the ratio between the longest and shortest distances between
elements or pins of a bond pattern within a repeating pattern. This
ratio is calculated as the longest distance divided by the shortest
distance.
As used herein, the terms "necking" or "neck stretching"
interchangeably refer to a method of elongating a nonwoven fabric,
generally in the machine direction, to reduce its width in a
controlled manner to a desired amount. The controlled stretching
may take place under cool, room temperature or greater temperatures
and is limited to an increase in overall dimension in the direction
being stretched up to the elongation required to break the fabric,
which in most cases is about 1.2 to 1.4 times. When relaxed, the
web retracts toward its original dimensions. Such a process is
disclosed, for example, in U.S. Pat. No. 4,443,513 to Meitner and
Notheis, U.S. Pat. Nos. 4,965,122, 4,981,747 and 5,114,781 to
Morman and U.S. Pat. No. 5,244,482 to Hassenboehler Jr. et al.
As used herein, the term "garment" means any type of non-medically
oriented apparel which may be worn. This includes industrial work
wear and coveralls, undergarments, pants, shirts, jackets, gloves,
socks, and the like.
As used herein, the term "infection control product" means
medically oriented items such as surgical gowns and drapes, face
masks, head coverings like bouffant caps, surgical caps and hoods,
footwear like shoe coverings, boot covers and slippers, wound
dressings, bandages, sterilization wraps, wipers, garments like lab
coats, coveralls, aprons and jackets, patient bedding, stretcher
and bassinet sheets, and the like.
As used herein, the term "personal care product" means diapers,
training pants, absorbent underpants, adult incontinence products,
and feminine hygiene products.
As used herein, the term "protective cover" means a cover for
vehicles such as cars, trucks, boats, airplanes, motorcycles,
bicycles, golf carts, etc., covers for equipment often left
outdoors like grills, yard and garden equipment (mowers,
roto-tillers, etc.) and lawn furniture, as well as floor coverings,
table cloths and picnic area covers.
As used herein, the term "outdoor fabric" means a fabric which is
primarily, though not exclusively, used outdoors. Outdoor fabric
includes fabric used in protective covers, camper/trailer fabric,
tarpaulins, awnings, canopies, tents, agricultural fabrics and
outdoor apparel such as head coverings, industrial work wear and
coveralls, pants, shirts, jackets, gloves, socks, shoe coverings,
and the like.
Test Methods
Grab Tensile test: The grab tensile test is a measure of breaking
strength and elongation or strain of a fabric when subjected to
unidirectional stress. This test is known in the art and conforms
to the specifications of Method 5100 of the Federal Test Methods
Standard 191A. The results are expressed in pounds or grams to
break and percent stretch before breakage. Higher numbers indicate
a stronger, more stretchable fabric. The term "load" means the
maximum load or force, expressed in units of weight, required to
break or rupture the specimen in a tensile test. The term "total
energy" means the total energy under a load versus elongation curve
as expressed in weight-length units. The term "elongation" means
the increase in length of a specimen during a tensile test. The
grab tensile test uses two clamps, each having two jaws with each
jaw having a facing in contact with the sample. The clamps hold the
material in the same plane, usually vertically, separated by 3
inches (76 mm) and move apart at a specified rate of extension.
Values for grab tensile strength and grab elongation are obtained
using a sample size of 4 inches (102 mm) by 6 inches (152 mm), with
a jaw facing size of 1 inch (25 mm) by 1 inch, and a constant rate
of extension of 300 mm/min. The sample is wider than the clamp jaws
to give results representative of effective strength of fibers in
the clamped width combined with additional strength contributed by
adjacent fibers in the fabric. The specimen is clamped in, for
example, a Sintech 2 tester, available from the Sintech
Corporation, 1001 Sheldon Dr., Cary, N.C. 27513, an Instron Model
TM, available from the Instron Corporation, 2500 Washington St.,
Canton, Mass. 02021, or a Thwing-Albert Model INTELLECT II
available from the Thwing-Albert Instrument Co., 10960 Dutton Rd.,
Phila., Pa. 19154. This closely simulates fabric stress conditions
in actual use. Results are reported as an average of three
specimens and may be performed with the specimen in the cross
direction (CD) or the machine direction (MD).
Strip Tensile: The strip tensile test is similar to the grab
tensile and measures the peak and breaking loads and peak and break
percent elongations of a fabric. This test measures the load
(strength) in grams and elongation in percent. In the strip tensile
test, two clamps, each having two jaws with each jaw having a
facing in contact with the sample, hold the material in the same
plane, usually vertically, separated by 3 inches and move apart at
a specified rate of extension. Values for strip tensile strength
and strip elongation are obtained using a sample size of 3 inches
by 6 inches, with a jaw facing size of 1 inch high by 3 inches
wide, and a constant rate of extension of 300 mm/min. The Sintech 2
tester, available from the Sintech Corporation, 1001 Sheldon Dr.,
Cary, N.C. 27513, the Instron Model TM, available from the Instron
Corporation, 2500 Washington St., Canton, Mass. 02021, or a
Thwing-Albert Model INTELLECT II available from the Thwing-Albert
Instrument Co., 10960 Dutton Rd., Phila., Pa. 19154 may be used for
this test. Results are reported as an average of three specimens
and may be performed with the specimen in the cross direction (CD)
or the machine direction (MD).
Peel test: In peel or delamination testing a laminate is tested for
the amount of tensile force which will pull the layers of the
laminate apart. Values for peel strength are obtained using a
specified width of fabric, clamp jaw width and a constant rate of
extension. For samples having a film side, the film side of the
specimen is covered with masking tape or some other suitable
material in order to prevent the film from ripping apart during the
test. The masking tape is on only one side of the laminate and so
does not contribute to the peel strength of the sample. This test
uses two clamps, each having two jaws with each jaw having a facing
in contact with the sample, to hold the material in the same plane,
usually vertically, separated by 2 inches to start. The sample size
is 4 inches wide by as much length as necessary to delaminate
enough sample length. The jaw facing size is 1 inch high by at
least 4 inches wide, and the constant rate of extension is 300
mm/min. The sample is delaminated by hand a sufficient amount to
allow it to be clamped into position and the clamps move apart at
the specified rate of extension to pull the laminate apart. The
sample specimen is pulled apart at 180.degree. of separation
between the two layers and the peel strength reported as an average
of peak load in grams. Measurement of the force is begun when 16 mm
of the laminate has been pulled apart and continues until a total
of 170 mm has been delaminated. The Sintech 2 tester, available
from the Sintech Corporation, 1001 Sheldon Dr., Cary, N.C. 27513,
the Instron Model TM, available from the Instron Corporation, 2500
Washington St., Canton, Mass. 02021, or the Thwing-Albert Model
INTELLECT II available from the Thwing-Albert Instrument Co., 10960
Dutton Rd., Phila., Pa. 19154, may be used for this test. Results
are reported as an average of three specimens and may be performed
with the specimen in the cross direction (CD) or the machine
direction (MD).
Martindale Abrasion test: This test measures the relative
resistance to abrasion of a fabric. The test results are reported
on a scale of 1 to 5 with 5 being the least wear and 1 the most,
after 120 cycles with a weight of 1.3 pounds per square inch. The
test is carried out with a Martindale Wear and Abrasion Tester such
as model no. 103 or model no. 403 available from James H. Heal
& Company, Ltd. of West Yorkshire, England. The abradant used
is a 36 inch by 4 inch by 0.05 thick silicone rubber wheel
reinforced with fiber glass having a rubber surface hardness 81A
Durometer, Shore A of 81 plus or minus 9. The abradant is available
from Flight Insulation Inc., a distributor for Connecticut Hard
Rubber, 925 Industrial Park, NE, Marietta, Ga. 30065.
Handle-O-Meter: The softness of a nonwoven fabric may be measured
according to the "Handle-O-Meter" test. The test used herein is the
INDA standard test 1st 90.0-75 (R 82) with two modifications: 1)
the specimen size was 4 inches by 4 inches and 2) five specimens
were tested rather than two. The test was carried out on
Handle-O-Meter model number 211-5 from the Thwing-Albert Instrument
Co., 10960 Dutton Road, Phila. Pa. 19154. The Handle-O-Meter
reading is on a scale of 1 to 5.
Hydrohead: A measure of the liquid barrier properties of a fabric
is the hydrohead test. The hydrohead test determines the height of
water (in mbars) which the fabric will support before a
predetermined amount of liquid passes through. A fabric with a
higher hydrohead reading indicates it has a greater barrier to
liquid penetration than a fabric with a lower hydrohead. The
hydrohead test is performed according to Federal Test Standard
191A, Method 5514.
DETAILED DESCRIPTION
Many different thermal bonding patterns have been developed for
nonwoven fabrics in order to give them integrity for further
processing into finished materials, for bonding to other materials
(e.g. nonwovens and films) and to impart particular visual markers.
Some patterns for sterile wrap applications, for example, provide
indicators to help show where the fabric should be folded. Patterns
for diapers and wipes can include "baby objects" such as bears,
trains, etc. More utilitarian patterns have been developed for
applications such as car covers and oil absorption materials.
One recently developed pattern is known as a point unbonded or PUB
pattern and includes unbonded fabric surrounded 100 percent by bond
area, an example of which is shown in FIG. 4. This pattern
generally may have a bond area of from about 25 to about 50
percent. The complete surrounding of an unbonded area gives this
pattern good abrasion resistance and nonwoven fabrics having this
pattern have found utility as, for example, the "loop" in hook and
loop fastening systems. Such fabrics may be found in the landing
zone on some Huggies.RTM. diapers. The complete surrounding of an
unbonded area is believed to significantly reduce fiber mobility by
tying down all loose ends within a small area. While useful for
many applications requiring toughness, fabrics with this pattern
can be somewhat stiff.
An older pattern is that known as an Expanded Hansen-Pennings or
"EHP" bond pattern. The EHP patterns has a bond area generally from
about 10 to about 30 percent, an example of which is shown in FIG.
2. Higher bond areas are possible but usually result in stiff
fabrics unsuitable for many applications. The EHP pattern does not
completely surround an unbonded area and so fiber mobility and
softness are greater than in a PUB fabric, however abrasion
resistance and strength are lower than a PUB fabric at the same
bond area.
In order to avoid the trade-off between abrasion resistance and
softness seen in the PUB, EHP and other patterns, the inventors
have developed a pattern wherein an unbonded area is not completely
surrounded by bond area but is surrounded to a large degree. This
pattern provides sufficient numbers of immobilized fibers to
strengthen the fabric, yet not so much as to increase stiffness
unacceptably.
Testing of fabrics bonded with an example of the inventive pattern
(called by the inventors "S-weave") and with EHP bonded fabrics
showed a surprising increase in abrasion resistance and hydrohead
with good strength and acceptable softness. Details of the fabrics
and the testing follow.
EXAMPLE 1
A laminate was produced using a nonwoven layer and a film
layer.
The nonwoven layer was a 20 gsm layer of fabric made by a spunbond
process with 2 denier fibers produced from a polypropylene
copolymer having about 3.5 weight percent ethylene. The copolymer
was produced by the Union Carbide Company under the designation
6D43. The nonwoven fabric so produced was thermally self bonded
with either the EHP pattern of FIG. 2 or the S-weave pattern of
FIG. 1.
The film was a multilayer film having a bonding layer and an outer
layer. The film was produced by coextrusion and had an overall
basis weight was 58 gsm. The bonding layer was made from about 55
weight percent Supercoat.TM. CaCO.sub.3 (available from English
China Clay of Sylacauga, Ala., and having a coating of about 1.5
weight percent of either stearic or behenic acid to enhance
dispersion of the filler), 45 weight percent Dow AFFINITY.RTM. EG
8200 low density elastomeric metallocene catalyzed polyethylene
having a density of 0.87g/cm.sup.3 and a melt index at 190.degree.
C. of 5 g/10 min. The outer layer was made of about 50 weight
percent Supercoat.TM. CaCO.sub.3, 45 weight percent DOWLEX.RTM. NG
3310 linear low density polyethylene having a density of about
0.918 g/cm3 and a melt index at 190.degree. C. of 3.5 g/10 min., 5
weight percent Dow low density polyethylene 4012, and about 2000
ppm of Ciba Geigy's B900 stabilizer.
The co-extruded film was stretched in the machine direction in a
single stretching operation to about 391 percent of its original
length. Prior to stretching, the film was pre-heated by passing it
around a series of rolls at about 49.degree. C. In the stretching
step, the film was held back by a slow roll at about 66.degree. C.
and drawn by a fast roll at about 21.degree. C. The stretched film
was then annealed by passing over another roll without stretching
at about 82.degree. C.
The stretched film and pre-bonded nonwoven were fed to a thermal
point bonder and laminated together using a heated pattern roll at
about 93.degree. C. and a smooth steel anvil roll at about
88.degree. C. with a nip pressure of about 175 pounds per linear
inch. The pattern roll used a baby objects pattern which imparts
about a 15 percent bond area to the laminate.
The resulting laminate made with the nonwoven fabric and film had a
basis weight of about 42 gsm. The laminate with the fabric having
an S-weave pattern had an unsupported hydrohead of about 95 mbar
when 1 drop of water of water emerged on the opposite side and an
MD peel strength of 226 gms. The laminate with the fabric having an
EHP pattern had an unsupported hydrohead of about 61 mbar when 1
drop of water emerged on the opposite side and an MD peel strength
of about 298 gms. Note that these results are averages for three
separate measurements.
EXAMPLE 2
Samples of the nonwoven fabric (only) from Example 1 were tested
for Martindale abrasion, Handle-o-meter, tensile strength, and grab
tensile. The results are given in Table 1.
TABLE 1
__________________________________________________________________________
Bond Basis Strip Tensile Handle-O- grab grab Martindale Area Weight
MD CD Meter MD pk CD pk Abrasion % osy grams MD CD gm gm scale 1-5
__________________________________________________________________________
S-weave 17.7 0.65 6717 3549 7 2.5 5061 3589 5 EHP 16.8 0.697 4373
2004 6.7 1.3 3867 2188 3
__________________________________________________________________________
Comparative Example 1
As a comparative example, samples of nonwoven fabric (only) made
from the same polymer as in the above Examples and having a
rib-knit (RK) pattern according to U.S. Pat. No. 5,620,779 and wire
weave (WW) pattern were tested in the same manner as in Example 2.
This information is shown below in Table 2.
TABLE 2
__________________________________________________________________________
Bond Basis Strip Tensile Handle-O- grab grab Martindale Area Weight
MD CD Meter MD pk CD pk Abrasion % osy grams MD CD gm gm scale 1-5
__________________________________________________________________________
RK 16.5 0.56 3551 3168 3.8 2 3988 3288 3 WW 18 0.59 4187 3234 7 3.3
2826 3366 4.4
__________________________________________________________________________
The results from the S-weave examples show an increase in strength
and abrasion resistance while maintaining acceptable softness.
Hydrohead in a laminate form with film also was increased. These
increases are quite surprising since both the S-weave and EHP
patterns have about the same bond area, bond density and basis
weight.
In alternative embodiments an S-weave patterned fabric or laminate
may be stretched in order to create perforations or apertures in
the material according to, for example, the neck stretching patents
cited above or U.S. Pat. No. 4,588,630 to Shimalla, U.S. Pat. No.
3,949,127 to Ostermeier et al. and U.S. Pat. No. 5,628,097 to
Benson et al. which involve stretching a fabric after patterning in
order to open the fabric at the bond points.
The S-weave type of pattern is best understood by examining the
aspect ratio of the elements or pins of the pattern as well as the
unbonded fiber aspect ratio.
Turning now to the drawings, note that the lines drawn on FIGS. 2
and 3 are for illustrative purposes only and do not form part of
the patterns. The elements or pins only form the patterns.
FIG. 1 is an example of a pattern fitting the requirements of the
invention. FIG. 1 has elements or pins 1 which are identical. The
pins have a center to center spacing 2 of 0.143 inches and a
minimum spacing 3 of 0.0288 inches. The pins are 0.012 inches wide
and 0.1226 inches long along the centerline.
FIG. 2 has a pattern of square tapered points 10 with a wide
spacing 11 of 0.0664 inches and a narrow spacing 12 of 0.0526
inches. The pins are all 0.037 inches across.
FIG. 3 has identical elongated oval shaped elements 20 which have a
width of 21 of 0.016 inches and length 22 of 0.031 inches.
FIG. 4 has fibers 30 completely surrounded by bond area 31 which is
shown diagonally lined.
The element aspect ratio for the EHP pattern shown in FIG. 2 is 1
since the length and width of the element are the same, i.e., the
bonds are square. The wire weave pattern of FIG. 3 has elements of
length 0.031 inches and width of 0.016 inches for an element aspect
ratio (0.031/0.016) of about 2. The element aspect ratio for the
S-weave pattern shown in FIG. 1, for example, is 0.1226/0.012
inches or about 10. Ratios as high as 20 and as low as 2 are
believed to work wherein ratios beyond these limits will suffer
from stiffness (more than 20) or lack of integrity (less than 2).
More particularly a ratio of between about 7 and 15 is desirable or
still more particularly, between about 8 and 12.
Also required is that the unbonded areas of the pattern be
sufficiently large. This ensures that enough fibers will be free
for use, for example, as a loop material for a hook and loop
fastening system. This also helps ensure that the fiber will not be
too stiff. In the case of FIG. 2, the unbonded fiber aspect ratio
is about 3 and in the case of FIG. 3 about 1.7. The S-weave pattern
of FIG. 1 has an unbonded fiber aspect ratio of about 5 as
calculated by 0.143/0.0288. Ratios as high as 10 and as low as 3
are believed to work, more particularly a ratio of between about 8
and 3 is desirable or still more particularly, between about 6 and
4.
The bond area is also important in describing the bond pattern of
this invention since a highly bonded pattern would be entirely too
stiff. The inventors have found that a bond area percentage of less
than about 30 percent is required, more particularly between about
10 and 25 percent and still more particularly between about 15 and
20 percent.
Another aspect of the S-weave pattern is the pin density of the
pattern. Some bonding patterns may have pin densities of as much as
500 pins per square inch, while the S-weave and EHP patterns are
generally in the 50-200 pin/in.sup.2 range, more preferably about
75-150, and, in the Examples, about 100. The patterns of U.S. Pat.
No. 5,620,779, for example, have pin densities in the 200-300
range, and the well known wire weave pattern usually has a pin
density of about 300, even when bonded with approximately the same
bond area as an S-weave or EHP pattern. The RK pattern and WW
patterns of the Comparative Example had pin densities of about 242
and 302, respectively. Its believed that higher pin densities with
about the same bond area tie down more fibers, i.e., reduce fiber
freeness, and so serve to stiffen a fabric and reduce softness.
The novel S-weave pattern may be used to self-bond fabrics and
should be distinguished from patterns made to laminate materials
together which are significantly different. The S-weave pattern may
be used with any thermally bondable fiber, monocomponent,
biconstituent, conjugate, coform etc.
The pattern of FIG. 1, for example, satisfies the requirements of
the invention and produces a fabric with abrasion resistance and
strength greater than a fabric bonded with a like amount of bond
area but without the required aspect ratios. The hydrohead for
nonwoven/film embodiments is also superior to fabrics having
similar bond area but aspect ratios outside of the invention
requirements.
Although only a few exemplary embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. In the claims, means
plus function claims are intended to cover the structures described
herein as performing the recited function and not only structural
equivalents but also equivalent structures. Thus although a nail
and a screw may not be structural equivalents in that a nail
employs a cylindrical surface to secure wooden parts together,
whereas a screw employs a helical surface, in the environment of
fastening wooden parts, a nail and a screw may be equivalent
structures.
It should be noted that this patent application is one of a series
of applications being filed on the same date, having the same
assignee, and incorporated herein by reference in their entirety.
In addition to the instant applications, these are:
"Stretch-pillowed Bulked Laminate Useful as an Ideal Loop Fastener
Component", inventors: McCormack and Haffner, Attorney docket no.
13520.
"Breathable Barrier Composite Useful as an Ideal Loop Fastener
Component", inventors: McCormack, Haffner and Jackson, Attorney
docket no. 13148.
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